Earthmoving machines (e.g., a track type tractor commercially available from Caterpillar Inc.) having earthmoving implements (e.g., a blade, such as a bulldozer blade) are used on worksites in order to alter a landscape of a section of land. The implement may be controlled by an operator of the machine to perform work on the worksite. For example, the operator may move a lever that controls the movement of the implement through hydraulic mechanisms coupled to the implement. Specifically, if an operator moves a lever within the machine, the movement of the lever translates into an electrical signal supplied to the hydraulic mechanisms. The electrical signal causes the hydraulic mechanisms to move, thereby transferring hydraulic pressure within a cylinder of the hydraulic mechanism. Because the hydraulic mechanisms are coupled to the implement, the transfer of pressure within the cylinder causes the implement to move in a manner consistent with the movement of the lever by the operator.
In addition to the hydraulic mechanisms, earthmoving machines also have a conventional engine and transmission, including gears, to maintain optimal performance of the engine. The transmission may be manual, in which the operator can physically change transmission gears with a clutch and gear shifter or lever. Alternatively, gears can be shifted electronically, in which the operator depresses appropriate buttons on a control panel, for example, to generate corresponding electrical signals to carry out a gear shift. Optionally, the operator may actuate a lever, which activates known circuitry to supply the gear shifting electrical signals. Electronic control transmissions change gears of the transmission through electronic control systems, such as a controller area network (CAN) as described in greater detail below.
Fixed gear transmissions often require synchronization of clutch disengagement, gear shift, and clutch reengagement to shift from one gear to another. Such synchronization, coupled with the weight of the machine, causes the machine to pitch or tilt when gears are shifted. The pitching can create instability in the implement position, causing the implement to move up or down in an uncontrolled manner. Moreover, if the implement is close to the ground and a down shift occurs, the implement may gouge the surface of the worksite.
In addition, when earthmoving machines perform coverage duties, such as covering a section of the worksite with material (e.g., loose rock), the machine typically operates more efficiently at a higher gear to empty and spread contents in the implement across the worksite. However, as contents are emptied and the operator switches to the higher gear, the machine may pitch upward thereby causing undesired spillage and uneven coverage of the material. Accordingly, to maintain even coverage, the operator may operate the machine in one gear, thereby decreasing efficiency.
The above-noted shortcomings can be overcome by manually operating the implement in compensatory manner to counteract the pitching of the machine. For example, if the operator shifts the machine from first gear to second gear, the operator may also simultaneously raise the implement to prevent gouging the surface of the worksite. Manual adjustment, however, requires that operators be experienced and skilled in knowing when and to what extent the implement should be moved during a gear shift. Moreover, since the hydraulic mechanism must first fill with fluid in order to move the implement, the implement may not respond fast enough to the operator's attempts to offset gear shift-related changes in implement position.
In addition, if so-called “control gains” associated with the electrical signals that control the hydraulic mechanism are low, the hydraulic mechanisms react slowly to the operator's controls, and may further hinder the operator's efforts to compensate undesired movement of the implement.
Although techniques are known for controlling implement position, none compensate effectively for implement movement during a gear shift, as discussed above. For example, U.S. Pat. No. 5,560,431 to Stratton et al. discloses an automatic control system of an implement, such as an implement, that accounts for changing ground profiles. The system of Stratton et al. detects a true ground speed of an earthmoving machine (e.g., a tractor). The system also senses an angular rate of the machine and senses the position of a lift actuator included with an earthmoving implement (e.g., a dozer blade). Based on such information, the system determines a slip rate value of the machine and a position of the implement as a function of the slip rate value, the angular rate, and the lift position. The position of the implement is then adjusted based upon this function. Stratton et al., however, does not adjust the implement in response to a gear shift of the transmission, and is thus susceptible to undesired implement movement, as discussed above.
The disclosed system is directed at overcoming one or more of the shortcomings in the existing technology.